The invention relates to a frequency response equalizer, particularly for wideband networks.
In wideband networks, for example, in cable television systems, wideband amplifiers are arranged in given cable sections for compensating the cable attenuation. In these networks amplification errors of a desired smooth frequency response may be caused by amplification tolerances in the frequency response of the individual amplifiers within a transmission path of the wideband network. Such amplification errors can be compensated by frequency response equalizers. To this end individual amplifiers within the transmission path may be preceded by attenuation members having a passband attenuation. Their attenuation can be eliminated in an adjustable frequency range by means of additionally available resonant circuits. To determine a passband attenuation, a series resistor may precede the amplifier. This resistor may be arranged in parallel with a series resonant circuit constituted by a resistor, a capacitor and a coil. The passband attenuation at a resonance frequency, which can be adjusted by means of the value of the capacitor, can be reduced or eliminated by means of the value of the resistor. The frequency behavior of such a frequency response equalizer can be negatively influenced by parasitic capacitances, for example, parasitic ground capacitances, because the parasitic ground capacitances and the coil constitute an interference resonant circuit. The smaller the capacitance of the capacitor of the series resonant circuit, the greater the interfering influence of the interference resonant circuit. In addition to the desired reduction of the attenuation at the resonance frequency of the series resonant circuit, an unwanted increase of the attenuation occurs, particularly at higher resonance frequencies. If the value of the capacitor approaches the value of the parasitic capacitances, the influence of the interference resonant circuit may become greater than that of the series resonant circuit itself, which leads to an unwanted increase of the attenuation at the interference resonance frequency instead of to the desired reduction of the attenuation at the resonance frequency of the series resonant circuit.